Addition compositions for acid electroplating baths

ABSTRACT

An addition composition for obtaining electrodeposited metallic coatings of high quality is prepared in accordance with the following method: A. Cellulose is degraded in a strong acid (such as H2SO4 or HCl in the presence of glycocoll and an alkali halide is added such as NaCl or NaF; b. A ketone (such as acetone) is mixed in an anhydrous medium having an alkaline pH value with a cyclic aldehyde (such as furfural) and with at least one-third compound selected from the group comprising the unsaturated alcohols, amyl aldehyde, cinnamic aldehyde and amylcinnamic aldehyde; an alkali sulphide or a thiol is then added in the presence of a mercury salt followed by halogenation and stabilization by addition of an oxidizing agent; C. The two products are mixed, then filtered and the clear liquor is retained. The present invention relates to the compositions used for making additions to baths in standard electroplating operations in order to obtain metallic coatings of better quality. The invention is primarily directed to a method of preparation of addition compositions. It is known that the aim to be achieved in electroplating work is to endow plated coatings with a number of properties, the relative importance of which changes according to the main purpose for which such coatings are intended. Up to the present time, it had proved virtually impossible to obtain all these properties simultaneously since such a result called for the realization of contradictory conditions both in regard to the nature and practical utilization of the bath. To be more precise, and to limit the discussion to one application such as nickel plating, for example, an ideal coating has good penetrating power (or in other words is capable of filling the porosities or cracks of the base metal), ensures uniform thickness, is nonporous (which entails a high surface density), has good adhesion, ductility and brightness. It had been considered heretofore that the two last-mentioned properties in particular called for baths having different characteristics and that these properties were therefore largely contradictory. The compositions of baths and conditions of deposition employed to produce ductile coatings resulted in dull or porous surfaces. Conversely, bright deposits invariably exhibited a porous structure or low ductility or both these deficiencies. One method which has been employed in particular for the purpose of obtaining bright coatings consists in the use of a nickel plating bath which contains the basic composition (nickel sulphate or sulphamate solution) as well as an addition of propane-sulphone or of sulphonic organic acids linked with a polymethylene radical. This bath lacks penetrating power and produces a nonuniform deposit which exhibits porosity as a result of the codeposition of the addition agent and is brittle by reason of high internal stresses which tend to be relieved only at the cost of failure of the plating. There has also been employed for the same purpose a bath containing adjuvants such as sulphamides, sulphimides, derivatives of coumarin, alkinoxyalkane and carboxylic acids, of chloral hydrate, in association with ethyl Or acetylene derivatives having a double or trip bond (Udylite or Harshaw baths). These baths have poor throwing power, result in only moderate penetration and cannot withstand high current densities in electrolytes which have low concentrations. The deposits are usually porous and nonductile, which makes it necessary in order to guard against corrosion to superpose two layers of nickel: the bottom layer is deposited with a different current density by employing a soluble anode in order to ensure a nonporous but mat surface. The surface layer is formed under conditions such as to ensure brightness but is nevertheless porous. Again in order to obtain bright deposits, acetylene derivatives have been employed as adjuvants with the addition of sulphonated derivatives (Kampschulte and Hanson van Wickle baths). However, the baths obtained have poor penetrating power and the deposits are highly porous. The baths contain compounds which have a multiple linkage with the carbon. The deposit does not offer any real guarantee against corrosion and has low ductility by reason of high internal stresses which probably arise partly from the presence of entrained organic substances in the deposit.

1 United States Patent Charrier [54] ADDITION COMPOSITIONS FOR ACID ELECTROPLATING BATHS [72] lnventor: Rene Charrier, 4 Avenue des Saules, 77,

Gretz-Armainvilliers, France [22] Filed:- Jan. 12, 1970 [21] Appl.No.: 2,406

[30] Foreign Application Priority Data Jan. 10, 1969 France ..6900327 [52] US. Cl. ...204/44, 204/DIG. 2, 204/43,

204/51, 204/52 R, 204/53, 204/54 R, 204/55 R [51] Int. Cl. ......C23b 5/46 [58] Field of Search ..204/DIG. 2, 43, 44, 45 R, 45 A, 204/46, 47, 48, 49, 50 R, 50 Y, 52 R, 52 Y, 53, 54

R, 54 L, 55 R, 55 Y, 51; 106/1; 117/130 E 56] References Cited UNITED STATES PATENTS 1,464,149 8/1923 Classen ..204/D1G. 2 2,149,344 3/1939 Hull ...204/D1G. 2 2,312,097 2/1943 Hull et al. ..204/49 1 Feb. 15, 1972 2,526,999 10/1950 Diggin et al ..204/50 Y 2,848,393 8/1958 Foulke et al.. .....204/50 Y 2,912,370 11/1959 Taverna ..204/50 Y Primary Examiner-G. L. Kaplan Attorney-Cameron, Kerkam & Sutton 57] ABSTRACT An addition composition for obtaining electrodeposited metallic coatings of high quality is prepared in accordance with the following method:

a. Cellulose is degraded in a strong acid (such as H2804 01' BC] in the presence of glycocoll and an alkali halide is added such as NaCl or NaF;

c. The two products are mixed, then filtered and the clear liquor is retained.

8 Claims, No Drawings ADDITION COMPOSITIONS FOR ACID ELECTROPLATING BATHS The present invention relates to the compositions used for making additions to baths in standard electroplating operations in order to obtain metallic coatings of better quality. The invention is primarily directed to a method of preparation of addition compositions.

It is known that the aim to be achieved in electroplating work is to endow plated coatings with a number of properties, the relative importance of which changes according to the main purpose for which such coatings are intended. Up to the present time, it had proved virtually impossible to obtain all these properties simultaneously since such a result called for the realization of contradictory conditions both in regard to the nature and practical utilization of the bath. To be more precise, and to limit the discussion to one application such as nickel plating, for example, an ideal coating has good penetrating power (or in other words is capable of filling the porosities or cracks of the base metal), ensures uniform thickness, is nonporous (which entails a high surface density), has good adhesion, ductility and brightness. It had been considered heretofore that the two last-mentioned properties in particular called for baths having different characteristics and that these properties were therefore largely contradictory. The compositions of baths and conditions of deposition employed to produce ductile coatings resulted in dull or porous surfaces. Conversely, bright deposits invariably exhibited a porous structure or low ductility or both these deficiencies.

One method which has been employed in particular for the purpose of obtaining bright coatings consists in the use of a nickel plating bath which contains the basic composition (nickel sulphate or sulphamate solution) as well as an addition of propane-sulphone or of sulphonic organic acids linked with a polymethylene radical. This bath lacks penetrating power and produces a nonuniform deposit which exhibits porosity as a result of the codeposition of the addition agent and is brittle by reason of high internal stresses which tend to be relieved only at the cost of failure of the plating. There has also been employed for the same purpose a bath containing adjuvants such as sulphamides, sulphimides, derivatives of coumarin, alkinoxyalkane and carboxylic acids, of chloral hydrate, in association with ethyl or acetylene derivatives having a double or trip bond (Udylite or Harshaw baths).

These baths have poor throwing power, result in only moderate penetration and cannot withstand high current densities in electrolytes which have low concentrations. The deposits are usually porous and nonductile, which makes it necessary in order to guard against corrosion to superpose two layers of nickel: the bottom layer is deposited with a different current density by employing a soluble anode in order to ensure a nonporous but mat surface. The surface layer is formed under conditions such as to ensure brightness but is nevertheless porous. Again in order to obtain bright deposits, acetylene derivatives have been employed as adjuvants with the addition of sulphonated derivatives (Kampschulte and Hanson van Wickle baths). However, the baths obtained have poor penetrating power and the deposits are highly porous. The baths contain compounds which have a multiple linkage with the carbon. The deposit does not offer any real guarantee against corrosion and has low ductility by reason of high internal stresses which probably arise partly from the presence of entrained organic substances in the deposit.

The object of the invention is to provide a composition which is intended to be added to electroplating baths and meets practical requirements more effectively than addition compositions employed in the prior art, particularly insofar as the resultant baths permit the deposition of metallic coatings which are endowed at the same time with all the properties of freedom from porosity, good adhesion, ductility and brightness.

To this end, the invention proposes in particular a method of preparation of an addition composition which is intended to be employed in acid baths for the electrodeposition of nickel, chromium, cadmium, zinc, gold, silver, platinum, copper, lead and tin or their alloys, wherein:

a. Cellulose is degraded in a strong acid (such as H SO or HCl) in the presence of glycocoll and there is added an alkali metal halide such as NaCl or NaF;

b. There is mixed in an anhydrous medium having an alkaline pH value a ketone (such as acetone) with a cyclic aldehyde (such as furfural) and at least one-third compound selected from the group comprising the unsaturated alcohols, amyl aldehyde, cinnamic aldehyde and amylcinnamic aldehyde; an alkali metal sulphide or a mercaptan is then added I in the presence of a mercury salt followed by halogenation and stabilization by addition of an oxidizing agent;

0. The two products are mixed, then filtered and the clear liquor is retained.

Among the properties of the addition composition mentioned above, it should be noted that, as a result of halogenation, said composition introduces only saturated bonds in the bath It is possible in particular to employ as ketone the acetone CH -,-CO CH and as unsaturated alcohol the propargyl alcohol HC I CCH OH. This operation is carried out in the presence of sulphur which is miscible in an organic medium supplied either by a sulphide or mescaptan such as one of the following compounds:

Ethylmercaptan (ethane thiol) CH;,CH,SH Dimethylsulphoxide Cl-I;,SOCH,- Tertiododecylmercaptan C, -H,,SH Thioacetic acid CH;,COSH Tetrahydrothiophene C H S Ethylene monothiocarbonate C -H,O,S

Ethane and propane dithiol HSCH,-CH,-SH and In practice, stage (b) is carried out and controlled in the following manner: the ketone fraction which is intended to be employed in this stage is mixed with aldehyde (furfural, for example) and with unsaturated alcohol (propargyl alcohol, for example) and possibly with a lower saturated alcohol such as denatured alcohol which is intended to perform the function of solvent having a low specific density soas to compensate for the specific density of furfural which is higher than that of water. Controlled chlorination or fluorination of the mixture is carried out in an anhydrous medium after having added the mercaptan or the sulphide and a mercury salt to the mixture: the reaction starts up progressively and has the effect of stopping the evolution of gas which is resumed after a period of 5 to 10 minutes and indicates completion of the reaction.

The color of the medium changes from pale yellow which is due to the sulphide to an amber shade which is probably due to the precipitation of a fraction of the sulphur, then to a greenish tinge if the reaction proceeds too far.

Stage (a) begins with the degradation of the cellulose in strong acid in the presence of glycocoll which acts as a stabilizer. The alkali chloride or fluoride is then added.

During this stage, the degradation of cellulose gives rise to hydrolyzed derivatives. It should be noted incidentally that it has already been proposed to add sodium salts of saccharine to the baths but that these products are costly, whereas the invention entails the use of degraded derivatives of cellulose which offer the same advantages while being extremely economical.

The addition composition which is thus obtained in accordance with the invention contains a large number of constituents, viz:

derivatives of acetone, in particular in the form of sulphonated and chlorinated or fiuorinated derivatives, degraded cellulose in the form of hydrolyzed sugars and aldehydes,

different saturated substances having large molecules.

In particular, the mixture of the two products obtained during stages (a) and (b) appears to produce an additional evolution during which a fraction of the degraded cellulose is combined with the products derived from the aldehydes.

It is very important to note that none of the compounds formed retains the double or triple bond which would result in deposits having either a porous or cracked structure. The signific'ance of this fact can readily be demonstrated: if only a very small proportion of a compound having a double or triple bond (butynediol, coumarin, propargyl alcohol) is added to a bath which contains the addition composition, the deposits again exhibit a porous structure.

The addition composition can be considered to have three characteristic properties: it does not contain any compound having a multiple bond; if sodium hydroxide is added, for example, in order to bring the composition to a pH value which is higher than 7, the solution becomes turbid but again becomes clear if it is brought back to an acid pH value; the addition of hydrogen peroxide to a bath which contains the addition composition not only does not destroy this composition but also regenerates this latter to a partial extent. And by way of example, the addition of one-eighth to one-fourth of cc./l. of bath (hydrogen peroxide having a strength of l 10 volumes) makes it possible to extend the life of the bath as expressed in ampere-hours by approximately 1/5.

EXAMPLE 1: Nickel plating baths There was added to nickel plating baths having a base of sulphate and of sulphamate an addition composition which was prepared by making use of the following proportions per liter of composition:

acetone: 20 to 300 cm.

propargyl alcohol: 10 to 100 cm.

denatured alcohol: 10 to 200 cm.

furfural: 10 to 200 cm.

sodium sulphide: 2 to 10 g.

mercaptan: 2 to 10 g.

cellulose: l to 10 g.

glycocoll: 2 to 100 g.

chloride or fluoride: l to 50 g.

chlorine or fluorine gas passed through the bath to excess:

10 to 100 g.

mercury bromide: traces hydrogen peroxide: 1 cm. at 1 l volumes.

By way of example, the proportion of addition composition which can be adopted varies between 0.10 cm. and 1 cm. per liter in nickel plating acid baths containing sulphate, sulphamate, chloride or fluoborate, the optimum proportion being evidently dependent on the concentration of the composition. An increase in the proportion results in a progressive increase in the ratio of metal deposited to hydrogen released but correlatively entails the need to adopt high current densities above a certain value. Since all the products employed in the composition are relatively stable, it is possible to operate at a temperature which attains 70 C. Current densities can be as follows in the case of a composition which is prepared from the following compounds (in respect of a quantity of 20 liters):

cellulose: 20 g.

acetone: 600 cm.

NaCl: 100 g.

denatured alcohol: 1,000 cm.

furfural: l,000 cm.

propargyl alcohol: 1,200 cm glycocoll: 100 g.

Na s: 200 g.

Hg: traces O H 2O cm. (hydrogen peroxide at 1 10 volumes) Current:

1 to 15 a./dm. in respect ofa content of0.3 cm. /l.

3 to 15 a/dm. in respect ofa content of0.5 cm. /l.

5 to 15 a./dm. in respect ofa content of0.8 cmf /l.

At 1 cm. /l., electrodeposition is carried out only at low current densities.

The pH value can be selected from a wide range which depends in any case on the type of coating which it is desired to obtain. A low value of the order of pH2 may be preferable in order to obtain a metal having a high value of hardness.

The plating bath which contains the addition composition can be employed either in a tank which has no partition or in a tank which is provided with a porous barrier between the anode and the cathode. Changeover to a low pH value can be carried out by addition of a mineral acid such as HCl or H 50 It is evidently feasible to combine the two methods by employing a soluble anode which permits a current density of 5 to 10 a./dm. in order to form a base coating, and then to employ a porous barrier in order to lower the current density to 0.l0.2 a./dm. and to form a corrosion-resistant surface layer. In general, the deposits obtained are nonporous and crackfree. Under suitable operating conditions, the coatings are both bright and penetrating (or in other words fill the porosities or fissures of the base metal) as well as being ductile and adherent if the base metal has been subjected to a correct surface preparation.

EXAMPLE 2 acid copper-plating bath.

The addition composition is prepared by means of the stages hereinabove defined by employing as starting products:

Denatured ethyl alcohol 50 cm: Acetone 20 cmf Propargyl alcohol 50 emf Furfural 50 cm. Mercaptans (dimethylsulphoxide 5 g. Cellulose 10 g. Glycoeoll 5 g. Excipient brought to 1 liter The pH of this bath can be adjusted by addition of boric acid.

The composition as thus constituted can in particular be added to the following baths in a proportion which is com- After neutralization, the last-mentioned bath is reacidified by hydrofluoric acid and the operating conditions are:

Temperature 40 to 60 C. Current density l0 to 20 aldm. Addition l to l0 cm./liter EXAMPLE 3: Plating baths for electrodeposition of a lead-tin alloy.

The addition composition is prepared from the following constituents, again by means of the same method.

Acetone 20 cmf Cinnamic alcohol 50 em.

Denatured alcohol 50 cm."

Mercaptan 2 g. (ethylene monothiocarbonate) Glycocoll 2 g.

Cellulose l0 Furfural l0 cm:

Current density 2 to 3 15 to 40 C.

EXAMPLE 4: Plating baths for electrodeposition of lead.

The addition composition as defined i employed with the following baths:

1. Lead fluoborate Free fluoboric acid Free boric acid Proportion Addition solution g to Example 3 Cifi nfde ii'sity Temperature 2. Basic lead carbonate 50% hydrofluoric acid Boric acid Current density Proportion of addition solution Temperature n Example 3 can be 200 to 250 g./l. to 30 gJl. 5 to g./l. 0.5 g to 5 all l to 2.5 a./dm. to C. 120 m 300 g./l. 150 m 500 g./l. 80 to 220 g./l.

0.5 to 8 aJdm.

0.5 to 5 g./I. 20 to C.

EXAMPLE 5: Plating baths for deposition of zinc.

' The addition composition is prepared from the following constituents:

Acetone 50 cm. Amyl alcohol 50 cm. Denatured alcohol 50 cm." Mercaptans 0.5 g./l

Furfural l g./l. Cellulose l0 g./l. Glycocoll 50 g./l.

The basic bath, operating conditions and proportion of adcan accordingly be dition composition contained in the bath as follows:

D ZINC PLATING.

l. Zinc fluoborate Ammonium fluoborate Ammonium chloride Current density Temperature Addition of Zinc sulphate Boric acid Ammonium sulphate Addition Current density Temperature Zinc Fluoborate Ammonium fluoborate Ammonium chloride Addition Current density Temperature Zinc fluosilicate Aluminum sulphate Ammonium chloride Temperature Current density Addition Dibasic potassium phosphate Potassium pyrophosphate Zinc sulphate (thioacetic acid 150 to 350 g./l. 301540 g./l. 20 to so g./l.

3 to 15 a.ldm. 5 to 4Q C. 0.2 to 2 g/l of addition composition 50 to 200 g./l. 10 to so g./l. [0 to 50 g./l.

l to 10 cc./l. 2 to 4 a./dm. 20 to 40 C. so w 200 g./l. so to I00 g./l. 10 to so g./l. l to 5 cell 3 to 20 aJdm. 20 to 30 C. so to 200 g./l. 5 to 30 l. 10 to 50 gl/l. 20 to 30" C.

3 to 7 a.ldm. 2 to 10 cc./l.

- 10 to 30 g-ll. I00 to 300 5..

50 to I00 g./l.

Ammonium oxalate or citrate l0 to 50 g./l. Ammonium sulphate 5 to 20 gJl. Addition 5 to 20 cc./l. Temperature 30 to 50 C. Current density 2 to 4 a./dm."

EXAMPLE 6: Gold plating baths The addition composition can be prepared from the following constituents:

in accordance with the invention is the following may be mentioned:

This composition can be added to of composition are also given:

I. Gold Chloride 4 to 20 g./l.

Dihasic sodium phosphate 20 to 200 g./l. Metabisulphite I to 5 g./l. Addition 0.5 to 5 cc./l. Temperature 40 to Current density 3 to 10 a./dm.

2. Citric acid 20 to 30 g./l.

Gold (in the double cyanide form) 8 to lo g./l. Current density 0.2 to 0.4 aJtlm: Temperature 40 to 55 C. Addition 0.5 to 5 cc./l.

EXAMPLE 7: Cadmiumplating baths The addition composition is prepared from the following constituents:

Acetone 20 cm Cinnamic alcohol 20 cm Denatured alcohol 20 cm 1 Mercaptans (propanedithiol l g. Glycocoll g. Cellulose 5 g. Furfural 10 cc Excipient for l liter The composition may be added in the proportions given to one of the following basic baths:

1. Cadmium sulphamate 200 to 300 g./l. Ammonium sulphate 30 to I00 g./l. Addition 10 to 50 cc./l. Temperature 20to 40 C. Current density l to 3 a./dm.

2. Cadmium carbonate 50 to I00 g./l.

Dibasic potassium phosphate 10 to 50 g./l. Sulphamic acid 5 to 30 cc./l. Current density 0.5 to 2 a./dm. Temperature 7 20 -30 C. Addition 5 to 20 cc./l.

3. Cadmium sulphate 200 to 300 g./l. Ammonia 100 to 300 g.ll. Addition 50 to I00 cc./l. Current density 1 to 2 a./dm. Temperature 18 to 25 C.

.Oxalic acid 10 to 30 cc.

Cadmium fluoborate 200 to 300 gJl. Ammonium fluoborate 50 to I00 g./l. Addition 5 to 20 cc./l. Temperature 18 to 30 C. Current density 2 to 5 a./dm.

By way of examples of application in which the composition particularly advantageous,

the deposition of a high metal;

the fabrication of printed circuits in which the higher degree of cohesion of the crystal grains and the formation of a smooth and adherent plating on the substrate (even on a metallized plastic material) reduces leakage currents;

reloading with hard nickel costly mechanical parts which are undersize;

deposition of coatings which afford resistance to atmospheric corrosion;

high density internal coating of tubes with a layer which is vacuumtight (and therefore withstand degassing), coatings having a low neutron capture cross section (maybe obtained from a bath which does not contain boric acid). It is understood that this composition must be employed in conjunction with compounds which are referred to as brighteningagent carriers and consist of naphthalene-sulphonic acid salts.

What is claimed is:

l. A method of preparation of compositions for addition to quality protective layer on a base one of the two basic baths given below, in which the operating condition and proportion their alloys to obtain plated coatings of better quality the steps of a. degrading cellulose in a strong acid selected from H SO and HCl in the presence of glycocoll and adding an alkali metal halide;

b. mixing a ketone in an anhydrous medium having an alkaline pH value with a cyclic aldehyde and with at least one third compound selected from the group consisting of the unsaturated alcohols, amyl aldehyde, cinnamic aldehyde and amylcinnamic aldehyde; then adding an alkali sulphide or a mercaptan in the presence ofa mercury salt; then halogenating and stabilizing the mixture by addition of an oxidizing agent;

c. mixing the two products of (a) and (b), filtering the mixture and retaining the resulting clear liquor.

2. A method according to claim 1, wherein the mercaptan is selected from the group consisting of:

Ethylmercaptan (ethane thiol) CH ,CH,-SH Dimethylsulphoxide CH SOCH Tcniododccylmercaptan C,,H,,SH Thioacetic acid CH CO-SH Tetrahydrothiophene C H,,S

Ethylene monolhiocarbonatc C;,H.O,-S

3. A method according to claim 1, wherein the alcohol employed is unsaturated propargyl alcohol.

4. A method according to claim 1, including the step of adding saturated alcohol ethyl alcohol during stage (b).

5. A method according to claim 1, wherein the cyclic aldehyde is furfural.

6. A method according to claim 1, wherein the alkali metal halide is selected from the group consisting of N aCl and NaF.

7. A method according to claim 1, wherein the halogenation of step (b) is carried out until an amber shade appears in the mixture.

8. A method according to claim 1, for preparing a composition to be added to a nickel electroplating bath, wherein step (a) is carried out using about g. of glycocoll and 100 g. of NaCl per 20 g. of cellulose and step (b) is carried out starting with 600 cm. of acetone, 1,200 cm. of propargyl alcohol, 1,000 cm. of furfural, 200 g. of Na S, and 20 cm. of hydrogen peroxide.

Ethane and propane dithiol 

2. A method according to claim 1, wherein the mercaptan is selected from the group consisting of: Ethylmercaptan (ethane thiol) CH3-CH2-SH Dimethylsulphoxide CH3-SO-CH3Tertiododecylmercaptan C12-H25-SH Thioacetic acid CH3-CO-SH Tetrahydrothiophene C4H8S Ethylene monothiocarbonate C3-H4-O2-S Ethane and propane dithiol HS-CH2-CH2-SH and CH3-CHSH-CH2-SH Dipropylsulphide C3H7-S-C3H7
 3. A method according to claim 1, wherein the alcohol employed is unsaturated propargyl alcohol.
 4. A method according to claim 1, including the step of adding saturated alcohol ethyl alcohol during stage (b).
 5. A method according to claim 1, wherein the cyclic aldehyde is furfural.
 6. A method according to claim 1, wherein the alkali metal halide is selected from the group consisting of NaCl and NaF.
 7. A method according to claim 1, wherein the halogenation of step (b) is carried out until an amber shade appears in the mixture.
 8. A method according to claim 1, for preparing a composition to be added to a nickel electroplating bath, wherein step (a) is carried out using about 100 g. of glycocoll and 100 g. of NaCl per 20 g. of cellulose and step (b) is carried out starting with 600 cm.3 of acetone, 1,200 cm.3 of propargyl alcohol, 1,000 cm.3 of furfural, 200 g. of Na2S, and 20 cm.3 of hydrogen peroxide. 